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Optonica SM-1515 Dead Channel

ringading

ringading

Well-Known Member
Picked this up at the local thrift for $20. It is in mint condition and I like the fluted knobs and overall solid construction.

Problem is it has a dead right channel - tried on headphones and speakers both and through Aux and Tuner inputs.

Right meter shows no life either - clue?

I have:
- Used Deoxit on the controls
- Switched the two power pack modules with no change
- checked driver transistors Q506, 508, 502 and double transistor Q504 with no chane
- replaced all electrolytic capacitors with the exception of the big can (dual capacitor)

Any suggestions? Should I continue working my way back through the path to Q404 etc?

upload_2016-7-29_16-13-1.png

I can start measuring voltage per the SM but I don't know enough to know what I am looking for.

Thanks all!
 
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I did check the fuses visually and with my DMM and they all check out good. Maybe I should replace to make sure? How do I check for rail voltage?

Is it one of these steps?

upload_2016-7-29_17-44-36.png
 
I don't know if anyone is paying attention to this thread anymore. I worked on some other projects and am coming back to this amp. I have checked all of the right side drivers including 508, 506, 504, 502 and 404 and all passed. I checked voltages per the schematic and all are within tolerances.

At this point I have no idea where to check next.
 
Checking back to see if anyone can suggest anything to check.

I did check what I think rail voltage is from pin 1 and 5 of each power pak to ground and each measures 38V/-38V and the schematic calls for 37.5/-37.5 so it seems that both paks are fine.
 
If the power amplifier checks out, then your problem is either further down the line or, most likely, at an earlier stage. Follow the schema to check wiring, muting functions, select switches, balance pots etc.

Bert
 
What you can do is build a simple audio tracker. With this you can track an input signal from source to the power amplifier. If the sound cuts out you have found your culprit.
 
Look at the more detailed schematic - rather than the simplified flowchart you have posted above. Look at the parts list and check to see if there are any fusible resistors listed. If there are - replace these if they test bad.
 
Well. If the STK was busted, I would expect either a fuse to snap, a protection circuit to activate or your mains fuse go pop. If none of this happens and swapping them does not change anything nor does that channel produce any sound at all (either hiss, static or otherwise) the most likely problem is that nothing is getting there. Most likely culprit would be a speaker fuse, wiring, a busted balance pot, a speaker select switch that is dirty, a problem in the pre-amplifier etc.

Another thing you may wish to check, however stupid this may sound: did you actually wire your speakers correctly? Is the dead speaker wired in it's posts? And is it wired in the correct outlet on the amplifier? I know it sounds stupid but it is a common mistake and i've slapped myself countless times for such a stupid and usually hurrying-to-get-wired mistake.
 
I am glad people are starting to notice this thread, Optonica equipment is mighty good and not common to find
 
Northwinds said:
I am glad people are starting to notice this thread, Optonica equipment is mighty good and not common to find
Click to expand...

That's right, it's fantastic equipment. I was lucky to 'score' an SM-4646 some years ago with the accompanying tuner and cassettedeck. It's made absolutely fantastic and plays better than most current high end systems. But mine has Sanken poweramp modules and i've scoured years to find two original sets as backups. That would be it's main problem, unobtainium parts. Huge dual capacitors in mine, should they fail it would require some interesting rework. I'd probably reuse the cans and rebuild their duality inside them with regular capacitors and extra vent holes. But every year I service them and aside from the smallest capacitors (which were replaced) literally everything is still on spec.
 
Glad to see a thread about this amp. I have the same one and this weekend I suffered the same problem: Right lane is out.

Did you arrive to any fix for it? I have _some_ idea bout electronics, but I don't have any oscilloscope or similar to generate a signal.

Thanks all!
 
First open the unit and check all fuses. There are many, I believe 6 at least. Each channel has it's own fuse with a very low amperage (200mA if i'm not mistaken). I would start there, it is the fuse that blows fastest when something happens that the amplifier thinks is uncool. Sometimes the fuse holder is a bit wonky, try to make it a tad tighter to hold the fuse. This for a 4646, not sure about anything lower.
 
Hey Bert, thanks for your reply! :)
I opened the unit today. I have a SM-1515. I found out that one of the 3.15A was blown (part F501 or F502 in the service manual). Good catch!
Looks like this model has 5 fuses in total (1.25A, 315mA, 3.15A x2, 2.5A)
This video helped me:


Not sure if it's allowed to upload the service manual in this forum. If someone needs it, please let me know.

Thanks again!
 
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Good to hear that it was 'just' a fuse. If it was an old fuse, the stress might have blown it. Otherwise, it's smart to look in the schema what feeds this particular fuse. A 3.15A fuse is rather large, not generally in the speaker relay in these Optonica machines.
 
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